Epidermal growth factor (EGF) is a small polypeptide which is synthesized and stored in the submandibular glands of mice and possesses a wide range of biological activities. After injection of EGF into newborn mice epidermal proliferation and keratinization is stimulated, the eyelids open prematurely, and the incisor teeth undergo accelerated eruption. Despite the use of accelerated tooth eruption in newborn mice as a bioassay for EGF the mechanism by which this phenomenon occurs has not been investigated. The present proposal includes 2 aims in order to define the possible role of EGF in neonatal tooth eruption and development. Aim 1: To determine the distribution and number of EGF receptors in the cellular compartments of the neonatal mouse incisor during the first two weeks after birth including ameloblasts, odontoblasts, outer and inner enamel epithelial cells, and pulpal and periodontal ligament fibroblasts. In addition, osteoblasts mesial to the first mandibular molar will be evaluated for the presence of EGF receptors. Aim 2: To determine the cellular response of the continuously erupting incisor of the newborn mouse to EGF administration in vivo by analysis of 3H-thymidine and 3H-proline incorporation into the cellular compartments of the developing incisor and the mandibular osteoblasts. It is anticipated that the completion of these aims will determine the location and number of EGF receptors in the developing tooth during the pre- and post-eruption period and delineate the cellular effects of EGF on the developing mouse incisor. In addition, the development of an autoradiographic localization technique for the developing incisor will allow for analysis of other types of receptors in future studies.